'''
Descripttion: 
version: 
Author: hewill
Date: 2021-11-14 20:24:48
LastEditors: hewill
LastEditTime: 2021-11-14 20:42:52
'''
import math
def binary_search(list, item):
    low = 0
    hight = len(list)-1

    while low < hight:
        mid = math.floor((low + hight)/2)
        guess = list[mid]
        if guess == item:
            return mid
        if guess > item:
            hight = mid -1
        else:
            low = mid -1
    return None

my_list = [1,3,5,7,9]
print (binary_search(my_list,3))
# print binary_search(my_list, -1)
